1. Field of the Invention
This invention relates to a display for sonars or radars, and more specifically, to a display for displaying the reflected wave information of a sonar or radar by a plurality of displaying light-emitting elements provided in a rotating member.
2. Description of the Prior Art
Cathode ray tubes have previously been used as displays for radars, scanning sonars, searchlight sonars, etc. A high-precision display based on a cathode ray tube is large-sized because of its inclusion of a mechanical driving section, and its weight is large enough to affect the mechanical strength designing of a place of its installation. Of course, such a display is not portable. On the other hand, a display built positively in a small size has an insufficient displaying ability and is difficult to view.
Attempts have therefore been made to use light-emitting elements such as LED as a display. One example is the technique described in Japanese Patent Publication No. 52268/1981. The use of light-emitting elements offers a solution to the problem of light-weight and small size in such displays. In a cathode ray tube display, a deflecting coil is rotated and information is received by a cathode in a fixed section. In a display based on light-emitting elements, information to be displayed should be transmitted to the light-emitting elements provided in a rotating member, and therefore, a mechanical contact portion should be provided in an electrical system.
The technique described in the above-cited Japanese Patent Publication No. 52268/1981 is one example of this type. In the device shown in it, a fixed disc having fixed contact pieces is disposed opposite to a rotating disc having light-emitting elements, and information received is transmitted from the fixed contact pieces of the fixed disc to the light-emitting elements of the rotating disc through a brush fixed to the rotating disc. The rotating speed of the rotating disc is about 20 to 30 revolutions per second, and the brush slides over the individual fixed contact pieces at a high speed. Hence, the on-off speed is fast. Because of this and also of the elasticity of the brush itself, chattering occurs at a very high frequency. In particular, when the light-emitting elements are light-emitting diodes, the persistence time is extremely short, and therefore the chattering makes it difficult to view the display and causes the fatigue of eyes. Furthermore, because of the high-speed sliding of the brush, the brush undergoes wear. The wear of the brush and the chattering roughen the surface of the contact pieces, and the service lives of the brush and the fixed contact pieces are shortened. This facilitates the occurrrence of the chattering.
The method of current collection by brushes has a mechanical limit when it is desired to increase its precision by increasing the density of arraying light-emitting elements. On the other hand, attempts to decrease the size of such a device while maintaining the same precision have not produced entirely satisfactory results because of the brushes and incidental parts.